1. Field of the Invention
The present invention relates to an LED (light-emitting diode) device, and particularly relates to a thin multi-layer LED array engine with enhanced light-mixing effect, which is capable of effectively dissipating heat generated in a phosphor layer.
2. The Prior Arts
The light-emitting theory of LED takes advantage of the intrinsic properties of semiconductors, which is different from the theory of electric discharging, heat and light-emitting of an incandescent light tube. Because light is emitted when electric current flows forward across the PN junction of a semiconductor, the LED is also called cold light. The LED has the features of high durability, long service life, light weight, low power consumption, and being free of toxic substances like mercury, and thereby it can be widely used in the industry of luminance equipment, and the LEDs are often arranged in an array and often used in such as electric bulletin board or traffic sign.
Please refer to Taiwanese Utility Model Patent No. M398686, which disclosed an airtight multi-layer array type LED packaging structure. FIG. 1 is a cross-sectional view of a conventional airtight multi-layer LED array engine packaging structure. Referring to FIG. 1, the airtight multi-layer LED array engine packaging structure includes a substrate 1a, an airtight metal frame 11a formed on the substrate la, a plurality of LED dices 5a formed on the top surface of the substrate la, a dice protection layer 7a, a phosphor layer 8a, and a silica gel protection layer 9a are sequentially formed on the LED dices 5a, and a dice protection layer 7a is formed on the LED dices 5a for protecting the LED dices 5a. The phosphor layer 8a is formed between the dice protection layer 7a and the silica gel protection layer 9a. The silica gel protection layer 9a is capable of preventing moisture from permeating into the phosphor layer 7a. Therefore, the phosphor layer 7a will not be deteriorated by exposure to moisture.
However, the conventional multi-layer array type LED package has un-uniform distribution of color temperature. The LED dices 5a emit light from different directions, and the light paths in the phosphor layer 8a are different, and thereby the distance past through the phosphor layer 8a is different. A part of the light emitted at large angle will be reflected by the sidewall of the LED package, and will enter the phosphor layer 8a again, and thereby the light path in the phosphor layer 8a will become long, so that the conventional LED package tends to emit light having light pattern with yellow halo phenomenon at the periphery.
Another disadvantage of the conventional multi-layer array type LED package is that heat generated in the phosphor layer 8a cannot be effectively dissipated out. Although the light source (i.e. the LED dices 5a) is spaced apart from the phosphor layer 8a, the phosphor layer 8a is still involved in radiation heat transfer from the LED dices 5a. However, heat cannot be effectively dissipated out from the phosphor layer 8a formed between the dice protection layer 7a and the silica gel protection layer 9a, and consequently, the phosphor layer 8a is deteriorated and has the problem of poor light mixing effect.
Therefore, there is a need to provide a thin multi-layer LED array engine, which has enhanced light-mixing effect, and is capable of effectively dissipating heat generated in a phosphor layer.